O.K. they say that on the application but I called and the rep told me differently. Stats courses given through social science departments are not sometimes comparable to stats courses given in the math department. Stats in soc science courses are less math-, formula-, and computation-based because usually the course is dedicated to stats in the context of research design. You spend half the course learning about eco for example and how to design research experiments and the other half analyzing these experiments with statistics. This is the reason the social sciences offer their own stats courses when it would be simpler to have all their students take stats in the math departments. I took my stats course through the psyc deparment and I had this same question.
Now, the AMCAS rep told me if they have concerns about how you classify your courses they don't waste their time calling up each school and investigating. They will go by the department the course is given in, which would be a social science. It's sort of your choice if you want to risk it or not. If AMCAS decides to change your classification then it will hold up your app for lord knows how long--getting on hold is the kiss of death. You have to make your own decision; but I'm inclined to say that because you took your stats course in an eco department--a liberal arts major that is based on math (although not in the same magnitude as say physics)--you are probably O.K. classifying it as a math course.
Good luck and I hope AMCAS doesn't give you too much hassle/